Follicular helper T (T FH) cells represent a distinct subset of CD4+ helper T (T H) cells specialized in providing help to B cells. They are characterized by their unique transcriptional profile (Bcl6), surface marker expression (CXCR5, PD-1, ICOS and CD40L) and cytokine production pattern (IL-21 and IL-6). T FH cells provide help to B cells both to form germinal centers (GCs) and to differentiate into memory B cells and plasma cells for generation of humoral responses. However, there is emerging evidence that implicates T FH cells in the development of various human pathologies, such as autoimmune diseases, immunodeficiency and lymphoma. This review focuses on the current progress in this area including mouse and human studies. A clearer understanding of the mechanisms of T FH cell-mediated immunity and pathology may be exploited for rational development of therapeutic strategies.